Pigmented thymic carcinoids: a clinicopathological and immunohistochemical study of two cases.

Two cases of pigmented thymic carcinoids are presented. The patients were two men, 32 and 47 years of age. The two patients were asymptomatic and the tumor was discovered on routine chest radiographic evaluation. The tumors were treated by surgical excision in both patients. Grossly, they presented as tan-white tumors without evidence of necrosis or hemorrhage or any visible pigmentation. Histologically, the tumors were characterized by a monotonous proliferation of tumor cells arranged in a trabecular or nesting pattern. The tumor cells showed moderate amounts of pale eosinophilic cytoplasm, round to oval nuclei, and inconspicuous nucleoli. Mitotic activity varied from three to eight per 10 high-power fields. In addition, both tumors showed prominent areas of intra- and extracellular dark pigment deposition. The pigment reacted positively with the Fontana-Masson stain and was negative for iron stain. Immunohistochemical studies performed in one case showed immunoreactivity of the tumor cells for chromogranin, Leu 7, and keratin. Synaptophysin and P53 immunostains were negative. Clinical follow-up was obtained in one patient who was alive and well 10 years after surgical resection. The presence of abundant melanin pigment in thymic carcinoids highlights an important pitfall for diagnosis in these tumors that should be taken into consideration in the evaluation of anterior mediastinal lesions.